why can't i join the multiplayer room? It always says "not connected". What should i do to fix this? thank you

are you using the latest version (4.95)

In general Not Connected either means, you have pinged from the server due to internet issues on your end or the server has crashed. Have you tried joining some of the public rooms? Or is it every room? It may also be your antivirus/firewall restricted the program from accesing the internet, i've personally had that problem before. As sSlight said it does matter which version you have e.x. you might not be able to connect with a version older than 3.x.x so make sure you have the latest version of toribash (As of this post 4.95, if you have steam say so, steam auto updates.)

It can also happen from typing your password in wrong, and trying to connect with it. Maybe that's the problem.

yea i use the latest version
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it happened in every room, i tried to re-login but still, doesn't affect the connection

Check your firewall and antivirus if it doesn't allow Toribash.

Also try to run Toribash as an administrator.